Reverb Pre-Delay & Decay Time (RT60) Calculator

Reverb Pre-Delay & Decay Time
(RT60) Calculator

A tool to calculate syncopated reverb pre-delay & decay (RT60) times.


BPM Synced Reverbs

What is BPM Syncing?

BPM Syncing is something that we usually associate with delays, where we can easily switch between note values such as 1/4 note or 1/8 note delays. but there are a whole host of other devices and parameters that benefit from being synced to the beat, which only allows us to adjust in milliseconds (ms). 

Sidechain compression is a common type of processing that most producers are familiar with. This is a process nearly all of us inadvertently tweak so it pumps in time with the project tempo.

Of course, we don’t have to sync things to every downbeat or bar, we could also sync sounds to 16th notes or similar, such as a typical 3/16 note delay.


How to Sync reverb pre-delay & decay times

To do this for parameters with millisecond values, we need to first calculate the beat divisions and their millisecond values for our projects bpm. 

For example, 120 beats per minute can be divided down into 500ms per beat (1/4 note). So from here, we can figure out that 1/16th note is 125ms, (more on the maths and simpler ways to calculate bpm beat divisions later).

This concept of synchronized parameter values can get really interesting when we apply it to our reverb pre-delay and decay times. Locking our reverb tails and other ambient noises in time with the beat adds life and additional groove into your music on an almost subconscious level and is much better than setting values randomly.

Why you should use this technique on your reverb 
pre-delays & decays

  • Add separation between sounds and reverb tails. This separation, in turn, will bring clarity to your sounds and can then be fine-tuned to push a sound closer or further away to the listener.
  • Solidify the depth of your mix without overly washing out your mix (if you do it correctly and choose sensible values for your tempo). 

Useful Information for Beat Synced Reverbs

It is always advised to adjust your reverb values by ear once you have calculated your tempo and beat divisions. The reason for this is simple, everyone’s music is different. from the dynamics, to the tempo, feel, instrumentation, and most importantly in this scenario, the noise floor & RMS (‘root mean square’ or average level of our music).

The RMS is important because this along with a few other factors is going to dictate when our reverb decays can no longer be heard. As a bit of background, a reverbs length is measured as the time taken till it’s level drops below -60dBs. This is known as the RT60.

If we had nothing but a metronome and a reverb, then our calculations would be perfect for syncing our groove, In a typical case where we have a busy project with a high RMS, our reverb decays will get lost (masked) in the mix significantly earlier than their actual RT60 times which we have set to be in sync with the project tempo.

This disparity between the real RT60 and the one we perceive will actually throw our reverb decays ever so slightly off. In most cases, this is almost unnoticeable and pleasant effect on the groove, but it is something we thought was worth mentioning just so it’s very clear that this is not a ‘set and forget’ method. Care and attention have to be paid to the subjective content of the project as well as whether you want the groove to ‘push’ or ‘pull’. 

Finally, don’t forget that your millisecond values are for a given tempo only, so if you decide to change your project tempo later on in the production process, you will have to re-calculate your reverb pre-delay and decay times. 

Calculating Reverb Pre-Delay & Decay

There are two ways we can calculate our reverb values. The first is the old-skool way using a calculator and simple formula, and the second is using the useful bpm calculation tool on this page.

Using The Formula

The formula is as follows:

60000 / project tempo = value of 1 beat (ms)

Using this value of 1 beat allows us to double or half this value to find out the values for a 1/2 note, or 1/8th note etc. 

Lets run through a typical example…

  • There is 60,000 ms in a minute.
  • 60,000 divided by your song BPM (in my case this is (120Bpm)
  • This gives us the value, in milliseconds, of 1 beat, (500ms for my tempo).
  • We can the double and half our values to create a table of beat divisions.

So the formula would look like this:

60’000 ms / 120 Bpm = 500 ms (1/4 note value)

1/2 note     = 500ms * 2 (1000 ms)
1/4 note     = 500ms (our project tempo in milliseconds)
1/8 note     = 500ms /2 (250 ms)
1/16 note  = 500ms /4 (125 ms)
1/32 note  = 500ms /8 (62.5 ms)

Things to be aware of is that this is assuming the music is written in a 4/4 time signature. When inputting values into your device parameters, remember that 1000ms = 1 second.

Using The Studio Slave Reverb Pre-delay Calculator

We understand that the above method is a bit tedious and a sure way to kill your creative workflow in its tracks if you are in the middle of writing a track. So we went through the trouble of creating a calculator application for you that even deducts that pre-delay from the decay time for you, so all you have to do is input the pre-delay and decay time values straight into your reverb device, optionally tweak the groove, then your good to go!


More About Reverb

What is Pre-Delay

Pre-delay is the time between the end of the initial source sound and the beginning of the first reflections (sound returning to your ears after bouncing off the closest surfaces) being audible.

Imagine you’re back on that stage in a large music hall. This time you stand on the very edge of the stage and shout “Hello world!” toward the center of the hall. There will be a brief pause before you hear the first noticeable reflections of your voice, because the sound waves can travel much further before encountering a surface and bouncing back. (There are closer surfaces, of course—notably the floor and the ceiling just in front of the stage—but only a small part of the direct sound will go there, so those reflections will be much less noticeable.)

Adjusting the pre-delay parameter on a reverb allows you to change the apparent size of the room without having to change the overall decay time. This will give your mix a little more transparency by leaving some space between the original sound and its reverb.

Another important factor in getting a great reverb sound is the pre-delay setting. Pre-delay is the amount of time before the onset of the reverberant field. Longer pre-delay settings will add more depth to the reverb when the dry signal is up front in the mix. Shorter pre-delay settings will attach the “wet” reverb to the dry signal more closely, with the wet/dry balance determining how distant the original, dry sound will appear to be.

A good guideline for setting pre-delay times is to match them to the size of the space you are setting up. Think 0–10 ms for smaller size spaces like an average-sized bedroom, 10–20 ms for medium-sized spaces, and over 20 ms for larger spaces like halls and churches.

Keep in mind that these ranges are relative to the tempo, pace and density of the production, so it is usually best to adjust pre-delay in the context of the whole mix rather than in solo.

What Defines The Size Of An Acoustic Space

The first parameters most people tend to adjust when setting a reverb are size or dry/wet. size determines the boundaries of the space in which the reverb will exist but the perception of size actually comes mostly from the timing of early reflections. 

Early reflections are the first set of delays that come directly from the floor, ceiling and walls. Their timing and frequency response send the necessary binaural cues that allow the listener to recognize a dimensional space. These early reflections tend are usually quite distinguishable as opposed to late reflections which is made up of a much more diffused set of reflections that make up the reverbs decay.

The best way to set the size of a space is to begin by adjusting the reverb’s mix control so that you only hear the early reflections, this is very straight-forward to do on Ableton Lives reverb device which has a dedicated mix control for both early and late reflections.

Now you can listen carefully to the defining part of the reverb, the early reflections. Once you have set these you can then add pre-delay to separate the original sound from the reverb.

in terms of acoustic space, adding pre-delay has the same effect as distancing the original sound source from the closest reflective surfaces (which usually defines a bigger space but could also give clues to the listener’s position in a space.

For example, a sound with almost no pre-delay, and a set of early reflections that have a first set of tight reflections, and another set of loose reflections a few milliseconds later would indicate a large room with a listener stood right in the corner, whereas a sound with a big pre-delay and all the early reflections sounding at a similar time would indicate a large room with the listener stood directly in the middle.

Now that we have the pre-delay and size set, we can adjust the mix and adjust our late reflections, which gives us a secondary indication on the type, density, surfaces and size of the room.

Understanding Pre-delay, Decay time & RT60

Understanding Pre-delay, decay time & RT60

When we calculate RT60 we need to remember that this is the total time taken in milliseconds for the reverb to reach -60dBs. 

Because real reverb is subjective to the acoustic space it is heard in, reverb times and characteristics change depending on:

  • The frequency content of the sound source
  • The room size
  • The original sounds location in the space
  • The listening position

This means that an RT60 also includes any pre-delay. So when we are calculating an RT60, we cannot just take this number and use it as our ‘reverb decay’ parameter in Ableton Live and then go and set the pre-delay to whatever we want. Instead, we should be choosing a sensible pre-delay value which matches the sonic environment we are trying to create.

Once we have chosen a pre-delay value, we then subtract this pre-delay value from the RT60.  This will give us our decay time value. Together these two values give us our total reverb time (RT60) which, if synced up using our reverb delay calculator, will be nicely synced to your project tempo. Just remember to also fine tune these values as you see fit to account for the groove & subjective material that you are applying reverb To.

Dry Vs. Wet Reverbs - Choosing The Right Type

Dry Vs. Wet Reverbs

Choosing The Right Type

Within the vast majority of professional mixes you will usually find a mixture of different reverb configurations and types. Often, these reverbs have been set-up for specific purposes, or specific instruments or groups. I.E – ‘Drum Room Reverb’,  ‘Wide Synth Verb’, or ‘Snare Tone/Body Verb’.

We can break our reverbs up into a number of different ways, but generally speaking, we have our ‘overt’ and ‘covert’ reverbs. Overt reverb is the obvious reverb we want to hear in the mix, and covert reverb is our very subtle, subconscious reverb that serves a purpose whilst being almost inaudible. These could also be referred to as our ‘dry’ reverbs, and ‘wet’ reverbs. 

Dry Reverbs are Shorter reverbs such as small rooms & tight ambient spaces. They serve purposes such as creating presence, clarity, separation between sounds, a sense of realism and very subtle but crucially important depth. They do this without audibly washing over the mix and are generally mixed at such a level that you don’t notice them when they are there, but you should notice the absence of them if you were to mute the reverb or the reverbs return track.

These reverbs are vital for the life of your mix and will usually be between 200ms – 800ms (tempo dependant).

Wet reverbs are Chambers, Halls, plates and other long reverbs with a lot more power and depth.  These will play a big part in the feel and tonality in the main parts of your track such as any lead instruments and vocals. The values used for these reverbs still give a strong indication of the size and character of your acoustic space, but these reverbs are here to be heard.

Be careful with the low-end frequency content and length of these reverbs, because they can very quickly wash out a track with muddy low/mid frequencies which will not only cloud the mix but will also kill off the rhythm and groove you have worked hard to create.

Getting the balance between dry & wet reverbs is not easy and takes time to understand. Not all your sounds should be drenched in reverb and not all your sounds should be treated with more than one reverb (however it is fine to do this to some sounds). Remember that the goal here is to create an acoustic space that the listener can picture using just their ears. We can understand that a distant sound is far away if we have a very up-close and present sound to compare it to. This means that we should have a good combination of dry and wet sounds in our mix, using dry and wet reverbs and varying dry/wet levels to achieve that mental picture we are trying to paint.

We can also use reverb devices as inserts on certain sounds which will allow us to slowly reduce the original source sound as we push up the dry/wet value. This can be a great way to really push sounds far into the distant background to help create a soundscape to build upon with up-front sounds.


Inserts vs. Send/Return Configurations

Inserting a reverb plugin directly to an audio track is the quickest way to add a reverb effect, but greatly limits your ability to process the source audio and reverb effect independently.

A send/return configuration is when we send a duplicated portion of our source audio to a completely new audio track known as a ‘return’ or ‘aux’. We can then affect this return track with completely wet (set to 100% wet) reverb, which we can then mix into the track. 

This opens up our options for processing and automation, and also means we still have the complete original signal in the mix as well as this 100% wet one. In some cases we may actually prefer to use a reverb as an insert effect as it allows us to easily dial in a reverb dry/wet setting that pushes the original sound into the distance (by reducing the ratio between the original and reverberated sound).

This technique works great for lost of different purposes such as distant tech house shakers to help fill out a mix, to atmospheric techno pads. The trick here is to make a firm decision when you add another sound or element to the mix, what role is this element going to play, an upfront sound, or a background element?